Essential HTML tags

Superstructure

Tag / Element Semantics Default presentation
html "root" element; all other elements must be enclosed (descend) from this element  
head Information about the document  
body The content of the document: can have only one!  
title The title of the document (appears in window/tab title depending on browser)

"Block" tags

Tag / Element Semantics Default presentation
p Paragraph of text (no modifications; inherit all)
h1 Header, level 1 font-size: 200%; font-weight: bold;
h2 Header, level 2 font-size: 150%; font-weight: bold;
pre Pre-formatted text; line breaks and multiple spaces will be rendered as given font-family: monospace;
ul Unordered list (items in arbitrary order)  
ol Ordered list (items in sequence)  
li List item margin-left: 2em; marker to left (bullet for ul; numbers for ol)
blockquote long quotations margin-left: 2em;
div none ("division" of document) (no modification)

"Inline" tags

Tag / Element Semantics Default presentation
b ??? font-weight: bold;
i ??? font-style: italic;
strong strong importance for its contents font-weight: bold;
em emphasized font-style: italic
cite reference to a creative work font-style: italic
q short quotation

/* surround with curly quotes */

q:before { content: open-quote; }
q:after { content: close-quote; }

a anchor: a hyperlink to another location color: blue; font-decoration: underline;
sub ??? vertical-align: sub; /* subscript */
sup ??? vertical-align: super; /* superscript */
span none (no modifications)